The Weiss Klimatechnik ULA.4 is a new generation of OT clean air canopies. It is installed as a unit inside the suspended ceiling of the OT and consists of an air outlet element (single-layer or double-layer or differential flow polyester fabric), the H14 (or H23) HEPA filters to DIN/EN 1822 at the ends, an anodized aluminum or stainless steel plenum with sound absorbers and an air circulation modules. The air circulation modules contains (in the direction of the flow) a circulating air intake using a stainless steel microfabric or polyester fabric, an F9 filter to DIN/EN 799, fans with non-return flap valves and air supply connection. The mode of operation is to the take the room air in the air circulation module, mix it in with the fresh air by the air conditioner and discharged into the plenum chamber located above the filtered-canopy.